The present invention relates to the control of the discharge current along the laser paths of a ring laser gyro and, more particularly, to a system for inhibiting the quenching of the laser beams in a ring laser gyro after a radiation event.
Ring laser gyros are used, for example, in inertial navigation systems and typically comprise a quartz block having a closed loop lasing path formed therein. The lasing path is filled with a suitable gas and then the quartz block is sealed. At least a cathode and two anodes are provided on the block having electrodes in communication with the gas in order to supply a discharge current in the lasing path to excite the electrons of the gas atoms. As a result, the electrons are excited to different energy levels thereby emitting photons to produce the lasing effect. Typically, two counterpropagating laser beams are produced around the close loop path. The two laser beams interfere with one another such that an interferometer senses the interference pattern resulting from the interaction between the two laser beams As the ring laser gyro experiences rotation, the interference pattern shifts Sensors are provided to sense the shift in the interference pattern so that the inertial guidance system can detect movement of the structure supporting the ring laser gyro.
Discharge current controllers are usually provided in order to regulate the discharge current between the cathode and the anodes. When the ring laser gyro is subjected to an extremely large transient nuclear radiation event, the ionization of the gas within the ring laser gyro can increase dramatically. This increase in gas ionization results in a significant decrease in the voltage drop between the cathode and anodes resulting in a substantial increase in discharge current. The discharge current control circuitry usually recovers from the radiation event before the extra discharge path ionization dissipates. The discharge current control circuitry will, therefore, reduce the higher discharge current flow before the extra gas ionization dissipates. When the radiation-induced ionization finally does dissipate, the current control circuitry frequently is unable to track the resulting rapid increase in voltage across the ring laser gyro electrodes. Thus, subsequent to the event, the extra radiation-induced ionization collapses causing a rapid increase in the voltage and a rapid decrease in discharge current. The discharge current control circuitry cannot respond quickly enough in order to keep the discharge current at a level which will support lasing. Consequently, as the extra radiation-induced ionization collapses, there will be insufficient current flow along the laser paths of the ring laser gyro to support lasing and, as a result, the laser beams will be quenched.